The present invention relates to an optical disk apparatus, and in particular, to an optical disk apparatus comprising an objective lens driving device for driving an objective lens converging light on a recording surface, in a focusing direction, a tracking direction, and an inclining direction of an optical axis of the objective lens.
To achieve appropriate recording and reproduction in optical disk apparatuses, in which the recording density is continuously improved, objective lens driving devices are required which drive an objective lens converging light on a recording surface of the optical disk apparatus, not only in a focusing and a tracking directions but also in an inclining direction of an optical axis of the objective lens, thereby correcting even the inclination of an optical disk. Such an objective lens driving device is disclosed in, for example, in JP-A-6-162540 specification or JP-A-10-275354 specification.
In JP-A-6-162540 specification, a support member for supporting an objective lens holder for free inclined movement is shaped like eight parallel straight lines having one end secured to a side surface of the objective lens holder and the other end secured to a supporting and fixing section of a base, and supports a movable portion for free movement and inclined movement in three directions: the focus direction, the tracking direction, and the inclining direction.
In JP-A-10-275354 specification, there are provided an objective lens and a pair of support members for supporting the objective lens and the pair of support members are disposed in a plane orthogonal to the optical axis of the objective lens. The pair of support members each have one end connected to the objective lens and the other end connected to a fixed portion. And, with respect to rigidity indicating how difficult it is for the objective lens to rotate around the direction orthogonal both to the optical axis and a longitudinal direction of the support member, the one end side of the pair of support members is less rigid than the other end side thereof.
In the optical disk apparatus, to promptly and accurately align, light converged by the objective lens in the focusing direction, the tracking direction, and the inclining direction of the optical axis of the objective lens, by consuming only a small amount of power, the operational sensitivity of the objective lens driving device in each direction must be improved so that when the device is operated in a predetermined direction, a cross action corresponding to movement in another direction is reduced.
When M denotes a moment that acts around the center of the support members supporting the movable portion including the objective lens, on the fixing section when a drive voltage V is applied, Ki denotes a spring constant of each support member, and Li denotes a distance from the center of the support members to the fixing position of each support member, a static operational sensitivity St in the inclining direction of the optical axis of the objective lens is expressed by:                     St        =                  M                                    V              ·                              Σ                i                                      ⁢                                          k                i                            ·                              L                i                2                                                                        (                  Equation          ⁢                      xe2x80x83                    ⁢          1                )            
where the subscript i denotes the order of one of the plurality of support members. This equation indicates that to improve the operational sensitivity in the inclining direction, the moment acting around the center of the support members must not only be increased, but the spring constant of the support members must be reduced, and the distance from the center of the support members to the fixing position of each support member must also be reduced.
In the above mentioned JP-A-6-162540 specification, however, the eight linear support members are secured to the side surfaces of the lens holder and the distance from the center of the support members to the fixing position of each support member is large, so that this device does not have a sufficiently improved operational sensitivity.
On the other hand, in the above mentioned JP-A-10-275354 specification, a pair of support members are used wherein one end side thereof is made less rigid than the other end side thereof to obtain an operational sensitivity in the inclining direction. With this configuration, however, the rigidity also decreases in the focusing direction and the tracking direction, and cross action is likely to occur when the center of the support members deviates even slightly from the center of the action of a driving force.
The present invention is achieved in view of these points, and it is an object thereof to provide an objective lens driving device that improves operational sensitivity and reduces cross action in the case when light converged by an objective lens is driven and controlled to propagate in a focusing direction, a tracking direction, and a inclining direction of an optical axis of the objective lens.
To attain this object, the present invention provides an objective lens driving device including: an objective lens for converging light on a recording surface of an optical disk; a lens holder for holding the objective lens; and a plurality of support members for supporting a movable portion including the lens holder in such a manner that the movable portion can operate relative to a fixing section in a focusing direction, a tracking direction, and an inclining direction of an optical axis of the objective lens, in which four of the plurality of support members are fixed to outer edge portions of the lens holder, and at least one of the positions where the other support members are fixed to one of the lens holder or a fixing position of the fixing section is located inside the four support members fixed to the outer edge portions of the lens holder. The four support members fixed to the outer edge portions of the lens holder can restrain cross action, which may occur during an operation in each direction, while the other support members disposed for the inclining operation are fixed inside the four support members fixed to the outer edge portions of the lens holder, thereby reducing the distance from the center of the support members and improving the operational sensitivity in the inclining direction.
Additionally, according to the present invention, the support members fixed inside the four support members fixed to the outer edge portions of the lens holder can each have a coil-shaped portion or two or more bent portions or two or more coil-shaped bent portions to reduce the spring constant of the support members and improve the operational sensitivity in the inclining direction.
The above configuration serves to reduce cross section and improve the operational sensitivity in the inclining direction, thereby enabling the objective lens driving device and the optical disk apparatus to be stably driven and controlled.